LOS ANGELES — Masked bandits have attacked and robbed Baja California tourists at least seven times in recent months, acting with paramilitary precision and making off with cash and expensive vehicles, it was reported Saturday.

It was unclear whether the attacks represent a trend in the popular vacation area, but they have worried some surf club owners enough to cancel operations. In one case, a woman said she was sexually assaulted in front of her boyfriend and in another, a family was held at gunpoint.

U.S. authorities have long warned Americans to be careful when visiting Mexico because of threats ranging from kidnappings to drug-related violence.

"Criminals have been known to follow and harass U.S. citizens traveling in their vehicles, particularly in border areas," said an October warning issued by the U.S. State Department.

The recent attacks, though, have been particularly harrowing, involving carjackings by heavily armed men who held their victims hostage for as long as several hours. Most took place at night along a 190-mile stretch of coastline between Tijuana and San Quintin.http://www.foxnews.com/story/0%2C2933%2C314504%2C00.html